The invention relates to a rapping mechanism for rapping or vibrating the electrodes, preferably the collecting electrodes, also known as collector electrodes, of a high-voltage supplied electrostatic precipitator for the cleaning of smoke gases from industrial plants, power plants, etc. Such rapping is necessitated by the fact that, due to the way in which the precipitator operates, dust is deposited on the precipitator electrodes which must consequently be cleaned regularly of this dust during operation. The cleaning is achieved by a transmission of impact energy to the electrodes thus exposing the latter to intensive vibration whereby the deposited dust is released.
The impact energy required for rapping or vibrating the electrodes is usually produced by a number of hammers being lifted by a rotating shaft extending across the precipitator width from their vertically suspended position and subsequently being released so as to revert to their vertical position. For each hammer an impact rod or an impact beam is provided which is hit by the hammer when the latter reverts to its vertical position and from the impact rod/beam the supplied impact energy is then transmitted to a section of precipitator electrodes.
The collecting electrodes usually consist of vertically suspended, narrow and substantially rectangular plates which, at their upper ends, are secured to a suspension device in a precipitator housing containing the electrodes. The latter may be arranged in mutually parallel rows or precipitator sections and the rapping is effected for the separate sections by means of drop hammers and impact rods for each section.
Rapping mechanisms of this type are known, e.g. from Duda: "Cement Data Book", 3rd edition, pp 596-598 (Bauverlag GmbH - Wiesbaden und Berlin 1985), and from patent disclosures Nos. U.S. Pat. No. 3,844,742 and EP-A-0,398,476.
In the so-called European type electrostatic precipitators drop hammers and impact rods which are connected to the lower ends of the collecting electrodes are generally used. This results in a disadvantage that the hammers and their carrier bridges occupy comparatively much space at the end of and below the precipitator sections which, in turn, presupposes an increased length and height of the precipitator housing containing the sections. In the so-called American type electrostatic precipitators the rapping of the electrodes is often effected from the top of the precipitator, the rapping mechanism then being mounted externally on top of the precipitator housing and the rapping being effected by means of small, vertically mounted impact rods which hit the electrode suspension device vertically. In this case each impact rod is provided with slide sealings around the passage through the precipitator housing roof. Certain types of "American" precipitators may alternatively be provided with a vertically acting rapping mechanism mounted inside the precipitator housing and which actuates the electrodes axially.
In order to avoid absorption of the impact energy by the precipitator housing construction the so-called European type as well as the American type precipitators may have insulators and protective spring elements, discs or leaf springs mounted between the housing construction and the rapping mechanism. It is a disadvantage of the American-type precipitators that a fracture in the rapping mechanism, which also acts as suspension device for the electrodes, may cause the latter to fall from the relevant precipitator section with the ensuing risk of causing a short-circuit and power cuts with a resulting precipitator shutdown. In case of American-type precipitators having the rapping mechanism mounted on top of the precipitator housing roof, the volume occupied by the aggregate precipitator construction in the relevant plant is substantially increased.
It is a further disadvantage of the above-mentioned hitherto known electrostatic precipitators that some of the impact energy which actuates the electrodes is immediately transmitted to the supporting construction of the precipitator construction thereby reducing the lifetime of the precipitator housing, irrespective of any optional damping of said energy by means of the inserted spring systems, and wherein energy which may usefully be used for electrode vibration is lost.
It is therefore the object of the present invention to provide a rapping mechanism for electrodes, preferably collecting electrodes, in an electrostatic precipitator, and which remedies the above-mentioned disadvantages of the prior art technique.